Maser



Feb. 27, 1962 P. F. CHESTER ETAL MASER Filed April 30. 1957 3 Sheets-Sheet 1 WITNESSES INVENTORS CBMQQQ, Q P E Chester and D -Bolef r ATT RNEY Feb. 27, 1962 P. F. CHESTER ETAL 3,023,366

MASER 5 Sheets-Sheet 2 Filed April 50, 1957 Feb. 27, 1962 P. F. CHESTER ET AL 3,023,356

MASER Filed April 30, 1957 3 Sheets-Sheet 3 2 H8 I .2 Tlme-- l C Fig I 2 D T 2 s; i z ,1 F G Noise Alone with Signal Noise and Signal Nise F' .12. A lg Time Radiation Density United States Patent 7 3,023,366 MASER Peter F. Chester and Dan I. Bolef, Penn Township, Allegheny County, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 30, 1957, Ser. No. 656,093

7 Claims. (Cl. 330-4) This invention relates to devices for amplifying or generating electromagnetic energy and more particularly to a device employing solids, liquids or gasesfor amplifying or generating microwave energyby stimulated emission of radiation.

Generally speaking, masers may be defined as devices for amplifying or generating wave energy by utilizing molecules in the excited state of a microwave transi tion. Interaction between these excited molecules and a microwave field produces additional radiation and hence amplification by stimulated emission. The operation of maser-s, such as the one described herein, is dependent upon the fact that in paramagnetic materials the electrons surrounding the nucleus of an atom may be in different energy states. These energy states may be thought of as arising from the interaction of the electron spins with internal or external fields. We may therefore refer to them as electron spin states. The energies of the electron spin states may be varied by an external magnetic field. Therefore, the energy difference between two given electron spin states is determined by the magnitude of the external magnetic field.

If a paramagnetic material having an excess electron spin population in a higher energy state is placed in a resonant cavity and if electromagnetic energy of appropriate frequency is fed into the cavity, the electron spins in the higher energy state will revert to a lower energy state,ithereby releasing energy which amplifies the signal fed into the cavity. In order to release the energy of the electron spins in the upper state to produce amplification, however, the original signal fed to the cavity must be of an appropriate frequency which is determined by the difference in the energy levels of electron spins in the upper and lower states; and this energy difference is, in turn, dependent upon the strength of the external magnetic field applied to the paramagnetic material. Thus, by varying the strength of the external magnetic field, the frequency at which the paramagnetic material will release its energy in the resonant cavity may be varied also. If the frequency of the electromagnetic signal fed into the cavity is not of the correct frequency to be amplified or if no signal is, introduced at all, the electron spins in the upper energy state, by interaction with their surroundings, will revert to a lower energy level over a time interval called the spin-lattice relaxation time.

It is an object of this invention to provide a new and improved solid state maser of the type described above. More specifically, an object of the invention is to provide a device employing magnetomechanical means to continuously furnish an excess upper state electron spin population in a paramagnetic material for continuously amplifying electromagnetic energy bystimulated einission. 1 j Another object of theinvention is to provide means, in a solid state maser, for producing a magnetic field profile on moving paramagnetic material whichvwillcreate an excess electron spin populationflinfan upper of two energy levels. Another object of the invention is to provide a solid statemaser employing an endless tape of paramagnetic material, or an endless tape having paramagnetic material placed thereon or combined therein to facilitate 3,023,366 Patented Feb.

2 continuously applying to the resonant cavity an excess electron spinpopulation in an upper energy state.

A still further object of the invention is to provide a solid state maser en ttploying a fluid containing paramagnetic material, and circulating through a closed path, to facilitate furnishing an excess electron spin population in the upperof twoenergy levels. A A still further object 'of the invention is to provide a solidstate maser which operates superregeneratively.

The above and other objects and features of the in-.

vention will become apparent from the following detailed description taken in connection with the accompanying drawings 'which fmm a part of the specification and in whichz 1 FIGURE 1 is a graphical illustration of the operation of the present invention; 1 I p v a FIG. 2 is an illustration of one embodiment of the invention; Anotherversion of a maser employing a rotating disc is described in a copending abandoned application, Serial No. 656,092; a

FIG. 3 is a sectional view taken along line ]1II]I of FIG. 2; 1 1

- FIG. 4 is a sectional view taken along line IV-IV of FIG. 2. FIG. 5 is a sectional view taken along line V-V of FIG. 2;

' FIG. 6 is an illustration of the preferred embodiment of the invention; l

FIG. 7 is a sectional view taken along line VII-VII of FIG. 6;

.FIG. 8 is a top view of another embodiment of the inven oni FIGS. 9A and 9B are cross sectional views taken along lines IXA IX A and IXB-IXB, respectively, of FIG. 8;

FIG. 10 is an illustration of the invention which operates superregeneratively; FIG. 11 is a graph illustrating a magnetic field profile traversed by the paramagnetic material in the embodiments of the invention outlined above as a function of time ordi'stance; and

FIGEIZ is agraph illustrating the radiation density in the restinant cavity of the superregenerative embodiment of the invention shown in FIG. 10, as a function of time.

Referring to FIG. 1, two energy states of electron spins in" a paramagnetic 'jmaterial are indicated by the horizontal-lines identified as' E and E Part of the electron spins in'the paramagnetic material will be at the lower energy state E while the remainder will be at the higher energy state E The paramagnetic material is in thermal equilibrium, corresponding to a normal or relaxed condition, when there is an excess electron'spin population in the lowerenergy state E Electron spins in the energy states E and E 'can interact with a microwave radiation field of appropriate frequency and either absorb energy from the' radiation field while advancing to a state of greater" energyor, under the'infiuence of the radiation field, can give up some of their energy and drop to a state of lower energy. The amount of energy thus transferred (i.e., E -E is related to the frequency of the radiation field by the following equation:

where h is Plancks constant and v: is the frequency.

If an electron spin in the lower energy state E1 is placed in a microwave field of appropriate frequency, it will absorbenergy andadvance tothe upper energy state E An electron in the upper state E on the other hand, will give up'energy to the microwave field and drop to the lower state E The probability for either transition is the same. Therefore, whether a system of many elec- 1 trons exhibits a netabsorption or emission of energy depends upon whether more electrons are in the lower or mined by the spin-lattice relaxation time, an excess electron spin population, exists in the lower state. A sufficiently rapid reversal of anexternal magnetic field will invert the energy levels-of the electrons such that the excess spin population now appears in the upper energy level E If the paramagnetic material with an excess spin population in the upper state is now passed through a resonant cavity and if electromagnetic energy F of a predetermined frequency is fed to the cavity, the electron spins in the upper state willrelease their energy, resulting in amplification of the incident wave energy to produce an amplified signal F.

A maser for amplifyingelectromagnetic energy by the process described above is shown in FIG. 2 and comprises a disk of paramagnetic material, or containing someparamagnetic atoms. or molecules, which is made to rotate about an axis 12. If preferred, only the outer periphery of disk 10-need be formed from paramagnetic material. A portion of the periphery of disk 10 lies between the opposite poles of a C-shaped electromagnet 14 which applies a steady magnetic field to the paramagnetic material and which has claws at the end thereof as shown in FIG. 5. At the same instant another portion of the periphery of disk 10 lies in a resonant cavity 16 which is located between theopposite poles of a second C-shaped electromagnet 18 which produces a field which is reversed with respect to the field produced by magnet 14, mag. net 18 having claws at the end thereof as shown in FIG. 5. I Electromagnetic energy is fed to the resonant cavity 16 through wave guide 20 and leaves the resonant cavity through the same wave guide or through another wave guide 22. From point A to point B, while the magnetic material is under the influence of the field produced by magnet 14, the elctronspins spend a long enough time to come almost to equilibrium in the strong field produced by magnet14. The time spent in magnet 14 may be reduced considerably by the use of techniques for reducing T where T is the spin-lattice relaxation time. One technique applies to those substances, e.g. doped silicon, which, when illuminated with light, release free carriers. Under such circumstances, T canbe reduced to the orderof a microsecond. A second technique for reducing T appliesto .those substances, e.g. paramagnetic salts, in which a doping agent can be used in such a way as to introduce a degeneracy in energy level spacingsbetween the host system and doping system for certain values of field or orientation. This produces an excess f of spins in the lower energy state E where f lower unuer N lower Nuvver and where and pw g is the splitting factor for the electron; a is the Bohr'magne'tron;

k is Boltzmanns constant; and.

T is the absolute temperature.

4 wave cavity 16 in the section F to G. The cavity is in the uniform steady magnetic field produced by magnet 18 and the magnitude of this field determines the frequency at which the electron spins will release their energy.

The magnetic field experienced by the paramagnetic material as it passes through the fields produced by magnets 14 and 18 is shown in FIG. 11. Between points A and B, the paramagnetic material is under the influence of the strong magnetic field H produced by magnet 14. Between points B and E in FIG. 11, the field experienced by an electron is rapidly reversed since the paramagnetic material passes rapidly from magnet 14 to magnet 18. Consequently, the minimum effective field H, is reversed in a time, T that is short compared to the Larrnor period L in that field. The minimum efiective field is the smallest field capable of lining up the electron spins. That is, it is roughly a field several times larger than the half width of the resonance line. This process inverts the energy levels of the electron spins and results in the excess population now being in the excited state, as was explained above. The spins then proceed into the microwave cavity 16 between F and G, during which time the. paramagnetic material is under the influence of the uniform steady magnetic field H the magnitude of which determines the frequency, V, of emission. Stimulated emission takes place in the cavity, with the result that the electromagnetic energy fed into the cavity from wave guide 20 is amplified and leaves the cavity either back throughguide 20 or through wave guide 22. Provided that the time taken from point B to point F is short compared with the spin-lattice relaxation time, the efliciency of' the process is high and not many excited spins are relaxed by interaction with the lattice during the time from B to F. After leaving the cavity, the spins proceed to electromagnet 14 where the process is repeated.

As an amplifier or spectrometer the gain of the device is proportional toN fQt/ v where N is the number of spins passing through the cavity per second;

f is the fraction defined above;

Q is the quality factor of the cavity;

v is the half-width of the resonance line; and

t is the transit time through the cavity.

Asa microwave generator, the maximum power output is proportional to Nfv. Thus the output increases with. increasing frequency and increasing peripheral speed. The factons determining the minimum speed of rotation are:

(1) That T L i.e. T I/v I where (2) That the time, T taken from B to F be only a fraction of T Assuming a field gradient at CD of 5X 10 gausses/cm. in the direction of motion and requiring that T =O.IL I, it is easy to show that the required peripheral velocity, S, is given by S=5.6 10 (H) cm./sec. Thus for H'=1 gauss, S=5.6 10 cm./sec., which for a disc 15 cm..in diameter corresponds to about 7,000 r.p.m.

For the distance B to F to be 3 cms. or longer and for s u e a pr ctica guessed With materials so far reported in the literature it is mechanically justfeasible to operate thedevice' atroom temperature, either as a high-gain amplifier or as a microwave generator with an output of about 0.1 watt at 3 mm} In this casethe working substance could be for example 10cc. of potassium chloride containing 10 F- centers per on a 30 cm. diameter disk-' rotating at 60,000 r.p.m., f:0.75% and T =2.5 10- seconds. Other materials, for which T has not been measured at room"temper'ature but which are expected to be an improvement on the above, are (a) diamond, boron nitride, ofsynth'etic sapphire doped-with paramagnetic impurities or containing paramagnetic centers as the result of irradiation, (b) silicon doped with lithium, arsenic, antimony, bismuth or phosphorus in any suitable concentra tion. I

As one goes to lower temperatures, T is considerably increased for all substances, so that in the above example the speed of rotation could probably be reduced to 15,000 r.p.m.--at liquid nitrogen temperature and at low enough temperatures to the limit set by the non-adiabatic field'reversaloondition, perhaps.5,'000 r.p.m.

For a microwave generator of reasonable poweroutput it is desirable to use a substance with the largest spin density'consistent with a line width less than about ga usses; At present it seems thatheavily doped silicon (up to 10 donors/cc), diphenyl-picryl-hydrazyl (10 spins/cc.) or diluted potassium chromicyanide (10 spins/cc.) may prove'to be the best materials for this application. i

For maximum gain in an amplifier wherev power output is not the prime consideration, low spin density is not a dis-. advantage if it is accompanied by aucompensatingnarrow line width. Materials having line widths less than one gauss .and with long enough relaxationtimes at liquid helium temperatures are bisulphates of graphite and certain organic free radicals, as well as substances exhibiting inhomogeneously broadened lines such as doped silicon and F-centers inalkali halide crystals.- These would also be chosen to minimize rotational speed when power is not the prime consideration.

The preferred embodiment of the instant invention is shown in FIGS. 6 and 7 and comprises acontinuous tape 50 of paramagnetic material, or having paramagnetic material deposited thereon, which is mounted on two spaced rotating, drums 52 and 54 so that the tape 50 is continuously moving. The tape moves through the field produced by a first electromagnet $6 to create an excess electron spin population in a lower energy state E as was explained above. The tape then moves into the resonant cavity 58 which is under the influence of the magnetic field produced by a second electromagnet 60, the field produced by electromagnet 60 being reversed with respect to that produced by electromagnet 56. Electromagnetic energy of a: predetermined frequency, determined by the strength of the magneticfield at the cavity 58 enters the cavity from Waveguide 62 andhhaving been amplified, leaves via waveguide 6401- back through waveguide 62. The principle of operation of the embodiment of this invention is the same as that'for the masses shown in FIGS. 1 -5 and the magnetic field' profile shown in FIG. '11 is traversed by the param'a'gnetic'material.

A further embodimento'fthe invention is shown in FIGS. 8, 9A and 9B and comprises a closed fluid circuit 100 containing a fluid medium incorporating electron spins. Th eiliquid passing through the circuit 100.may be a liquid which exhibits electron spin paramagnetism suchas a liquid metal ammonia solution or .it may be .an inert liquid containing ats olid paramagnetic material.

Asan alternative, it may be a paramagnetic .gas, such as oxygen or theoxides of nitrogen,:0r, it may be an inert gas carrying solid paramagnetic lparticles in. suspension. A'Estill furtheral'ternative would bextouse a liquid refrigerant, such as liquid nitrogen, asa carrier for oxygen or another paramagnetic gas. The fiuid' in circuit first passes through the steady magnetic field produced by electromagnet 102 from point A to point B to create an excess electron spin population in the lower energy level E From point B to E, the fluid passes rapidly from the field produced by magnet 102 to that produced by el'ectromagnet104. Once in the field of magnet 104, it passes through the resonant cavity 106. Since the field produced by electromagnet 104 is reversed with respect to that'produced by magnet 102, an excess electron spin population is produced in' the higher energy level E and electromagnetic energy entering cavity 106 from waveguide 108 leaves the cavity as amplified wave energy via- Waveguide 110 or 108.

An embodiment of-the present invention which operates superregeneratively in shown in FIG. 10. This embodimentof the invention operates upon a principle similar to that shown in FIGS. 1-5 and comprises a disk 210 which rotates about an axis 212. The periphery of the disk, as was the case with the masses shown in FIGS} 1-5, first passes through the magnetic field produced by electromagnet 214 and then passes through the resonant cavity 216 which is situated in the magnetic fluid'produced by electromagnet 218, the field produced by magnet 218 being reversed with respect to that produced by magnet 214. Electromagnetic wave energy enters the cavity 216 via waveguide 220 and leaves as amplified wave energy via waveguide 222 or 220.

In FIG. 10 a the paramagnetic material is placed around 'theperiphery of the rotating disk 210 in discrete' and separate sections 224. 'For a disk which is 15' centimeters in diameter, 100 or more sections 224 ofparamagnetic material could be equally spaced around the periphery of the disk. The sections must be widely enough spaced so'that only one section can be in the cavity 216 at a given time, and so that the radiation density in the cavity due to one section has fallen to a low enough level before the arrival of the next section. When the density of spins in any section is greater than that necessary to cause oscillation build-up in the cavity due to noise or incoming signal, the device can operate superregeneratively.

The operation of the superregenerative maser' shown in FIG. 10 is graphically-illustrated in FIG. 12. It can be seen that the radiation density builds up as each section 224 passes through'the cavity and then subsides before the next section'passes through the cavity. In this way, each time a section leaves the cavity oscillation'build-up is'terminated.

The amplitude of oscillation after a given time interval depends in a definite way upon the magnitude of the radiation of the proper frequency present during the sensitive portion of the cycle. In FIG. 12 the build-up of oscillation with noise alone in the cavity during the sensitive portion of the cycle (shaded area) is compared with that with noise plus signal. For a disk rotating at a thousand revolutions per second, the quench frequency' or pulse repetition rate will be of the order of 100 -kilocycles. This can be improved by spacing the sections e224 more closely around the periphery of the disk 210. Q1ienching, or cut-off, comes about automatically because of the mechanical removal of the section from the cavity.

path j'and having paramagnetic material continuously disposed along the, length thereof, said tape member movingv at. a predetermined speed,ysaid paramagnetic material having two discrete energy levels of electrons, said electrons undergoing transitions between said two energyrlevels when subjected ,toelectromagnetic wave energy ofsaid predetermined frequency, first magnetic field producing means disposed in predetermined position withrespect to a first portion of said path for subjecting the paramagnetic material on the adjacent portion of the tape to a first magnetic field of predetermined magnitude anddirection, second magnetic field producing means disposed adjacent the first magnetic field producing means and in predetermined position with respect to a secondportion of said path, said portion of thetape moving from the first portion of the path substantially directly tothe second portionof the path, the second magnetic field producing, means producing on said portion of the tape -while,said portion is adjacent thereto. a second magnetic field of predetermined ma nitude and of a direction opposite to the direction of'the first magnetic field, the speed of movement of said tape being such that any point on the tape moves from the first magnetic field to the-second magnetic field in a time which is short compared to the Larmor period of the paramagnetic material, the sudden reversal of the polarity of the magnetic fieldon the'paramagnetic material as the paramagnetic-material on thetape moves from the first magnetic field to the second magnetic field causing state preparation in the paramagnetic material with an excess of electrons having high energy spin states and occupying the upper of said two energy levels, resonant cavity means resonant at said predetermined frequency disposed in, predeterminedposition with respect to a portion of the path of said tape and in predetermined position with respect to said means for producing a second magnetic field, said tape passing through said resonant cavity means, and means connected to the resonant cavity means for supplying electromagnetic waveenergy to be amplified to the resonant cavity means and conducting electromagnetic wave energy from the resonant cavity means, said portion of said tape passing through said resonant cavity means before spin-lattice relaxation occurs in the paramagnetic material in said portion of said tape, at least some of the electrons with high energy spin states in the paramagnetic material while in the resonant cavity means giving up energy to the electromagnetic wave of predetermined frequency as said last named electrons revert to the lower energy level thereby amplifying said electromagnetic wave, the continuous movement of paramagnetic material through the first and second magnetic fields as the tape moves providing continuous state preparationand providing for continuous amplification .of said electromagnetic wave energy.

2. Apparatus for amplifying electromagnetic wave energy having a predetermined frequency by stimulated emission of radiation, comprising, ,in combination, a continuously moving tape member moving in a predetermined path and having paramagnetic material continuously disposed along the length thereof, said tape member moving at a predetermined speed, said paramagnetic material having two'discrete energy levels of electrons, the electrons of the paramagnetic material undergoing transitions between said two energy levels when subjectedto electromagnetic wave energy of said predetermined frequency, first magnetic field producing means disposed in predetermined position with respect to a first portion of said path for subjecting the paramagnetic material on the adjacent portion of the tape -to a first magnetic field of predetermined magnitudeand direction, said speed being selected whereby any minute area of the tape remains in said first magnetic'field, for a period of time sufficient to induce;substantially. ,complete relaxation of electrons in theparamagnetic; material therein, second magnetic field producing means disposed adjacent the first magnetic producing means in predetermined position with respect to a second portion of said path, said area of the tape moving from the first portion of the path substantially directly to the second portion of the path, the second magnetic field producing means producing a second magnetic field of predetermined magnitude and of a direction opposite to the direction of said first magnetic field, said area moving from the first magnetic field to the second magnetic field in accordance with the speed of movement of the tape in a time short compared to the Larmor period of the paramagnetic material, the passage of the paramagnetic material from the first magnetic field to the second ma netic field whereby the paramagnetic material undergoes a sudden field reversal causing state preparation in the paramagnetic material with an excess of electrons having high energy spin states and occupying the upper of said two energy levels, resonant cavity means resonant at said predetermined frequency disposed in predetermined position with respect .to a portion of the path of said tape, and means for conducting electromagnetic wave energy ofsaid predetermined frequency to and from said resonant cavity means,v said area of said tape passing through said resonant cavity means before spinlattice relaxation occurs in the paramagnetic material in said area, 'at least some of. the electrons with high energyspin .statesin the paramagnetic material while in'the resonant cavity means giving up energy to said electromagnetic wave of predetermined frequency as said last named electrons revert to the lower energy level thereby amplifying said electromagnetic wave, the continuous movement of paramagnetic material through the first and second magnetic fields as the tape moves providing continuous state preparation and providing for continuous amplification of said electromagnetic wave energy.

3. Apparatus for amplifying electromagnetic wave energy having a predetermined frequency in a predetermined portion of the electromagnetic wave energy spectrum by stimulated emission of radiation comprising, in combination, a conduit having a paramagnetic fluid medium continuously passing therethrough, said paramagnetic fluid medium having two discrete energy levels of electrons, the electrons of said paramagnetic fluid medium undergoing-transitions between said two energy levels when subjected to electromagnetic wave energy of said predetermined frequency, means disposed in predetermined position with respect to a first portion of said conduit for subjecting the fluid meduim in the first portion of the conduit to a first magnetic field of predetermined magnitude anddirection, means forming a resonant cavity for electromagnetic wave energy of said predetermined frequency disposed in predetermined position with respect to a second portion of said conduit whereby said cavity is in the path of said moving fluid medium, means for subjecting said resonant cavity and the fluid medium passing therethrough to a second magnetic field of predetermined magnitude and which is reversed in direction with respect to said first magnetic field, any portion of the fluid medium moving from the first magneticfield to the second magnetic field in a time which is short compared to the Larmor period of the paramagnetic material, thesudden magnetic field p0- larity reversal on the paramagnetic fluid medium as it moves from the first magnetic field to the second magnetic field causing state preparation with an excess of electrons having high 'energy 'spin states and occupying the higher of said two energy levels, and means for con- 'veying electromagnetic 'wave energy of said predeter- "relaxation occurs in -.thevparamagnetictmaterial as said 9 last named electrons revert to the lower of said two energy levels thereby amplifying said electromagnetic wave of predetermined frequency, the continuous movement of the paramagnetic fluid medium through the first and second magnetic fields providing continuous state preparation and providing for continuous amplification of said electromagnetic wave energy. a

4. Apparatus according to claim 3 in which the paramagnetic fluidmedium is' disposed in a circulating fluid refrigerant for maintaining the paramagnetic material at a temperature approaching absolute zero to thereby increase the spin-lattice'relaxation time of the paramagnetic material.

' field producing means adjacent the first field producing means for subjecting said moving material and paramagnetic se ctionsto a second magnetic field of predetermagneticfield in a time short cdmpared'to the Larmor period of the paramagnetic material, the sudden reversal of the polarity of the magnetic field on the paramagnetic 5. Apparatus 'for amplifying electromagnetic waveenergy of a predetermined frequency by stimulated emission of radiation comprising, in combination, a conduit having a paramagnetic fluid medium therein, pump means connected to the conduit, said conduit and pump means forming a continuous path for-the flow of said paramagnetic fluid medium, said paramagnetic fluid medium having two discrete energy levels of electrons, said electrons undergoing transitions between said two energy levels when subjected to electromagnetic wave energy of said predetermined freguency, means disposed in predetermined position with respect to a first portion of said conduit for subjecting the fluid in said first portion of the conduit to a first magnetic field of predetermined magnitude and direction, means forming a resonant cavity resonant at said predetermined frequency and disposed in predetermined position with respect to a second portion of said conduit adjacent said first portion whereby said cavity is in the path of said moving fluid medium, the fluid medium passing into said second portion after passing through the first portion, means for subjecting said resonant cavity and the fluid medium passing therethrough to a second magnetic field of predetermined magnitude and which is reversed in direction with respect to said first magnetic field, the speed of flow of the paramagnetic fluid medium being such that the fluid medium passes from the first portion of the conduit to the second portion of the conduit in a time short compared to the Larmor period of the paramagnetic material, the sudden reversal of the direction of the magnetic field causing state preparation in the paramagnetic fluid medium with an excess of electrons having high energy spin states and occupying the higher of said two energy levels, and means for conveying wave energy of said predetermined frequency to and from said resonant cavity, at least some of the electrons with high energy spin states in the fluid medium in the resonant cavity giving up energy to the electromagnetic wave before spin-lattice relaxation occurs in the paramagnetic material as said last named electrons revert to the lower of said two energy levels thereby amplifying said electromagnetic wave, the continuous movement of the paramagnetic fluid medium through the first and second magnetic fields providing continuous state prep-aration and providing for continuous amplification of said electromagnetic wave energy.

6. In apparatus for superregeneratively amplifying electromagnetic wave energy of predetermined frequency by stimulated emission of radiation, in combination, a continuously moving material moving at a predetermined speed, discrete similar sections of a paramagnetic material carried at substantially equally spaced intervals by said moving material, said paramagnetic material having two discrete energy levels of electrons, said electrons undergoing transitions between said two energy levels when subjected to electromagnetic wave energy of said predetermined frequency, first magnetic field producing means disposed in predetermined position with respect to the moving material for subjecting the sections of paramagnetic material carried by the moving material to a transverse magnetic field of predetermined direction and magnitude as the sections move into position adjacent the first magnetic field producing means, second magnetic material of said last named discrete section causing state preparation in the paramagnetic material of said last named section with an excess of electrons having high energy spin states and occupying the higher of said two energy levels, means forming a resonant cavity positioned withinthesecond magnetic field and in predetermined position with respect to the continuously moving material wherebythe discrete sections of paramagnetic material are carried-through the resonant cavity while subjected to the second magnetic field, said cavity being resonant at said predetermined frequency, and means for conducting electromagnetic wave energy of said predetermined frequency to and from said resonant cavity, at least some of the electrons with high energy spin states in the discrete paramagnetic section in the resonant cavity giving up energy to the electromagnetic Wave before spinlattice relaxation occurs in the paramagnetic material of the last named section, the density of the electrons with high energy spin states in the discrete paramagnetic sections being greater than that necessary to cause oscillation build up in the cavity due to noise and a signal of said predetermined frequency, the speed of movement of the continuously moving material being preselected whereby said last named discrete section of paramagnetic material moves out of the resonant cavity after a predetermined time interval to provide for damping of electromagnetic wave energy developed in said cavity while the discrete section was disposed therein.

'7. In apparatus for superregeneratively amplifying electromagnetic wave energy of predetermined frequency by stimulated emission of radiation, the combination of a rotating disc rotating at a predetermined speed, a plurality of similar discrete sections of paramagnetic ma:- terial carried on the outer periphery of said rotating disc at substantially equally spaced intervals, said paramagnetic material having two discrete energy levels of electrons, said electrons undergoing transitions between said two energy levels when subjected to electromagnetic wave energy of said predetermined frequency, first magnetic field producing means for subjecting said disc and the paramagnetic sections carried thereby to a first transverse magnetic field of predetermined direction and magnitude, second magnetic field producing means disposed adjacent the first magnetic field producing means in the path of the rotating disc for subjecting the paramagnetic sections to a second magnetic field of predetermined magnitude and reversed in direction from the first magnetic field, any paramagnetic section moving from the first magnetic field to the second magnetic field in a time which is short compared to the Larmor period of the paramagnetic material, the sudden reversal of the direction of the magnetic field on said paramagnetic material causing state preparation with an excess of electrons with high energy spin states and occupying the higher of the two energy levels, a resonant cavity resonant at said predetermined frequency located in said second magnetic field, said rotating disc passing through said resonant cavity, and means for conducting electromagnetic wave energy of said predetermined frequency to and from said resonant cavity, at least some of the electrons with high energy spin states in the discrete paramagnetic sections giving up energy to the electromagnetic wave before spinlatticerelaxation occurs in the material, the density of the electrons with high energy spin states in the discrete paramagnetic sections being greater than that necessary to cause oscillation build up in the cavity due to noise 1 l and a signal of said predetermined frequency, said disc rotating at said predetermined speed whereby any discrete section of paramagnetic material remains in the resonant cavity a predetermined time interval and is moved out- References Cited in the file of this patent UNITED STATES PATENTS 2,762,871 Dicke Sept. 11,1956 2,802,944 Norton Aug. 13, 1957 2,836,722 Dicke et al May 27, 1958 2,851,603 Dicke Sept. 9, 1958 2,851,652 Dicke Sept. 9, 1958 2,879,439 Townes Mar. 24, 1959 OTHER REFERENCES Strandberg: Proceedings of the IRE, January 1957, pages 92-93.

Publication, Physical Review, vol. 91, N0. 5, Sept. 1, 1953, pages 1066-1078, Electronic Structure of F Centersin Electron Spin Resonance.

Publication, Physical Review, vol. 99, No. 4, Aug. 15, 1955, pages 1264-1274 The Maser and New Type of Microwave Amplifier, Frequency Standard, and Spectrometer.

Publication, Transactions of the Institute of Radio Engineers Professional Group on Electron Devices, PGED-3, June 1953, pages 1-4.

Translation of article in Comptes Rendes, Proceedings of the French Academy of Sciences, May 14, 1956, 1st semester, vol. 242, No. 20, pages 2451-2453.

Feher et al.: Physical Review, vol. 105, No. 2, January 1957, pages 760-763.

Wittke: Proceedings of the I.R.E., vol. 45, March 1957, pages 291-316. 

